Transparent electrodes are utilized in organic electronic devices. Such a transparent electrode is arranged on a light-receiving surface side of a photoelectric conversion element of which typical examples include organic solar cells. Such a transparent electrode is arranged on a light-emitting surface side of a light-emitting element of which typical examples include organic EL (electroluminescence) elements.
Indium tin oxide (ITO) has been frequently used as a transparent electrode material. ITO contains indium oxide (In2O3) and a small percent of tin oxide (SnO2).
A method of producing a transparent electrode comprising ITO is disclosed in, for example, Document 1. Specifically, an ITO application liquid formed by dispersing fine ITO particles in a solvent is prepared. The ITO application liquid is applied onto a substrate. The ITO application liquid on the substrate is heated at from 400 to 800° C. to form an ITO film (transparent electrode).
As described above, the transparent electrode comprising the ITO film is formed by baking at the heating temperature described above. Therefore, it is necessary to prepare the substrate having heat resistance that enables the substrate to endure the baking temperature. The heat resistance of organic functional layers (electricity-generating layers or light-emitting layers) included in organic electronic devices is low. Accordingly, it is impossible to form the transparent electrode comprising the ITO film on such an organic functional layer.
Conductive polymer layers have been developed as transparent electrodes having low baking temperature. Examples of the conductive polymer layers include PEDOT/PSS layers. Such a PEDOT/PSS layer is disclosed in, for example, Document 2. Such a PEDOT/PSS layer is produced by the following method. A dispersion liquid formed by dispersing poly (3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS) in water or the like is prepared. The dispersion liquid is applied to a substrate, and the substrate is dried. The PEDOT/PSS layer is formed by the above steps.
Document 3 proposes a transparent conductive film containing metal nanowires, as a transparent electrode substituted for such ITO films and such conductive polymer layers. The transparent conductive film disclosed in Document 3 contains a plurality of metal nanowires, and an ionizing radiation curable resin. The average diameter of the metal nanowires is from 40 to 100 nm, and the metal nanowires are contained in the transparent conductive film. The metal nanowires are, for example, silver. In the transparent conductive film, the metal nanowires intersect each other to form a network structure. As a result, a conductive path is formed, and the conductivity of the transparent conductive film can be obtained. Because the metal nanowires form the network structure, transparency can be obtained. The transparent conductive film of Document 3 is formed by applying a coating containing the metal nanowires onto a substrate or an organic functional layer, and curing the coating by irradiation with light, or drying the coating in a manner similar to that of Document 2.
In addition, transparent electrodes, or members corresponding to transparent electrodes are also disclosed in Documents 4 to 8.
For a solar cell which is one of organic electronic devices, Document 9 discloses that a stainless steel sheet is used as a substrate for a dye-sensitized solar cell. Document 10 discloses a solar cell in which a chromium-containing ferritic steel sheet is used as a substrate, and in which CIGS (compound containing copper (Cu), indium (In), gallium (Ga), and selenium (Se) as main raw materials) which is one of compound semiconductors is used. Document 11 discloses a silicon-based solar cell in which a stainless steel sheet is used as a substrate. Document 12 discloses an organic thin-film solar cell in which a cell structure is formed on a glass substrate using an organic thin film.    Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2009-123396    Document 2: JP-A No. 2013-185137    Document 3: JP-A No. 2012-216535    Document 4: JP-A No. 2012-219333    Document 5: International Publication No. WO 2010/106899    Document 6: Japanese National-Phase Publication (JP-A) No. 2006-527454    Document 7: JP-A No. 2013-152579    Document 8: JP-A No. 2011-86482    Document 9: JP-A No. 2012-201951    Document 10: JP-A No. 2012-97343    Document 11: JP-A No. 2011-204723    Document 12: Organic Electronics, 13 (2012) 2130-2137